It is known that in electric cells of this type, the anode reagent consists of an alkaline metal, generally sodium, which must be liquid at operation temperature. The cathode reagent generally consists of sulphur and sodium salts of this substance, but may alternatively be phosphorus, selenium and alkaline salts of these substances. In the case where the reagent materials are sulphur and sodium, the electrochemical reaction leads to a reversible formation of polysulphides whose sodium content increases during the discharge. As for the electrolyte, which separates the cathode and anode reagents, it must be solid at operation temperature and permeable to alkaline ions which form in the anode compartment but impermeable to electrons. It generally consists of beta sodium alumina, i.e. a compound having about 5 to 9 alumina molecules for one sodium oxide molecule. It is generally in the shape of a tube closed at its bottom, containing the anode reagent and immersed in the cathode reagent, the latter reagent being contained in a metal cathode tank. The electrolyte tube is held by a support connected in a fluid-tight manner to this cathode tank and also to an anode reagent tank.
Generally, this support is in the form of a plate or disk made of alpha alumina. This disk has a central bore in which the beta sodium alumina tube is fixed by means of a glass part, such as described by the Applicant in his French patent application N.degree.73 37 066 of Oct. 17, 1973.
Now, inasmuch as concerns the connection between the electrolyte tube support disk and the cathode tank and anode tank the latter is formed, as described in the above-referenced patent application, by ceramics-metal brazing.
However, although the connections formed in this way have good mechanical characteristics as well as high chemical resistance to the aggressivity of the reagents, the applicant has further improved such connections, with a view to providing them with better mechanical and thermal qualities.
Prefered embodiments of the invention provide a method for producing a sodium-sulphur type electric cell in which the connection between the various components is further improved and has, moreover, excellent resistance to the aggressivity of the reagents.
The invention therefore relates to a method of producing a sodium-sulphur type electric cell having the following construction.
A cathode tank contains a cathode reagent which is liquid at operation temperature and is selected from the group formed by sulphur, phosphorus, selenium and alkaline salts of these substances.
At least one solid electrolyte tube is closed at its bottom end, contains an anode reagent which is liquid at operation temperature and consists of an alkaline metal and is disposed in said cathode tank so as to be immersed in said cathode reagent with the walls of this tube being made of beta sodium alumina.
A support made of an insulating ceramics substance holds said electrolyte tube in said cathode tank with the connection between this support and this tube being provided by a glass part;
An anode tank containing a store of said anode reagent and is disposed above said cathode tank, so that said electrolyte tube opens at its top part in this anode tank and said plate separates the open ends of said anode tank and of said cathode tank.
The method of manufacturing said cell involves the following steps.
First the connection is formed between said electrolyte tube and said support made of an insulating ceramics substance.
Successively, said tanks are disposed on either side of said support made of an insulating ceramics substance by means of flanges provided at their open end and substantially concentric with said electrolyte tube, and an O ring is inserted between the end of the walls of the tanks and said ceramics support.
The assembly is then heated to a temperature close to but lower than the melting point of the material constituting said O ring while maintaining pressure on said flanges.
The assembly is then cooled down to ambient temperature. The invention is further charaterized by at least one bushing being previously disposed in contact with at least the internal bottom part of the wall of each of said tanks with said bushing resting on said insulating ceramics support.
An embodiment of the invention is described by way of example, with reference to the accompanying drawings.